Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Mar Sat 25, 2017 12:44 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 23 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 1:49 pm 
Member

Joined: Aug Thu 23, 2012 5:25 am
Posts: 129
Does anyone know if there are any AM stereo radio stations out there? I picked up a 1987 Dodge radio that has AM stereo on it..I heard an AM stereo station back in the late 80's and it sounded pretty darn good.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 2:11 pm 
Member

Joined: Aug Sun 01, 2010 1:12 am
Posts: 8387
Location: Minnesota
Not that I'm aware but around here, very few stations ever made the switch anyway. Haven't heard anything about it for a long time.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 2:48 pm 
Member
User avatar

Joined: Feb Sun 02, 2014 9:13 pm
Posts: 1454
Location: Roanoke, VA
For a list of AM stereo stations see:

http://users.hfx.eastlink.ca/~amstereo/amsstations.htm

Note that the list is not current - it was apparently last revised in 2001, and I know os somw US stations on that list that no longer transmit in stereo.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 2:53 pm 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 5693
I have no idea how current this information might be... http://meduci.com/stations.html

One would assume that if these stations are still operating in Stereo it would have to be the C-QUAM system.

Here is a comparison of C-QUAM and Digital stereo. https://www.youtube.com/watch?v=KA5vz0i8Loo

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 3:14 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 18989
Location: Utica, NY 13502 (USA)
Eickerman wrote:
I have no idea how current this information might be... http://meduci.com/stations.html
A note at the bottom of the web page says it was updated in July of 2016.

One of the requirements for stations applying for a license in the "expanded" AM band (1610 - 1700) when it was first authorized was that they promise to sign on with AM stereo. I see many stations in that band on the 2001 list but very few on the 2016 list. Comparing the lists, seems like many US stations across the whole band have turned their AM stereo off perhaps because it is incompatible with the IBOC digital technology.

Dave


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Mon 02, 2017 10:58 pm 
Member

Joined: May Sat 12, 2012 1:33 pm
Posts: 1180
Location: Rochester, NY.
The clear-channel C-QUAM stereo stations that I used to listen to are now all monaural. At night, I could capture 50kw AM stereo signals some 500 miles away with no problem:
https://en.wikipedia.org/wiki/C-QUAM

Some AM stations advertise as HD now. HD does not stand for hi-def, but is a name that iBiquity trademarked for their IBOC service (more distortion?):
https://en.wikipedia.org/wiki/HD_Radio

The AM stereo war for market dominance was won by giant Motorola over other systems that may have been better.
The Kahn system only needed a 2nd conventional AM receiver tuned to one sideband while the other receiver was tuned to the other sideband for left and right channels.

NDXE wanted to be the 1st shortwave station to broadcast in stereo using the Kahn system, but it never came to fruition.
I saved a few '80's-'90's Chrysler AM stereo/FM stereo radios up in the attic for posterity.

Europe has converted to DRM to conserve space on the crowded AM band over there. I hope that AM is working out better for them:
https://en.wikipedia.org/wiki/Digital_Radio_Mondiale


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Wed 04, 2017 6:09 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
AM stereo can be excellent I know this because I have demonstrated it with the same frequency response as fm and can even take it to 20khz if you like. The trouble is this. The majority of the radios are terrible. Change the I.F. band width to something decent and then listen to a stereo broadcast. If you build your own transmitter you can open up your radio's bandwidth and transmit to it and you will be very surprised. I have a setup here and have fooled people into thinking they were listening to anything but am. Then when I show them it is am they are in a state of oh wow i never would have believed it if you told me it could be done. The other thing that is needed is a good noise blanker not a new technology but a dsp noise blanker and all that and fm would die a quick death. Wider response possible but the fcc needs to re assign channels to do this. No buffering no delays am can be better covers more area per watt so (greener hehehe) cna be made far better than it is but the will is not there but the technology has been there for a long time.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Wed 04, 2017 8:03 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 23634
Location: SoCal, 91387
AM stereo came along about a decade too late, or it might have caught on. And IIRC when it did come along, it was ridiculously expensive to either add on, or for a new receiver.
No surprise that it's practically non-existent now, when music fare has largely deserted to FM. Why bother with stereo broadcasting when all that's left on AM are talk programs about news, politics, sports, religion, or in a foreign language?

Audioman, I don't think that I've ever seen a circuit diagram for a homebrew AM stereo transmitter; you got one?

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Wed 04, 2017 1:07 pm 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 13827
Location: Dayton Ohio
AM Stereo was a disaster.

It was proposed back in the early 1960s along with FM Stereo. Leonard Kahn proposed his independent sideband system at the time.

The FCC felt it best to give Stereo to FM only to help foster growth, and leave AM monaural.

Then in the early 80s, the FCC looked into AM Stereo again, and adopted Magnavox's system as I recall.
The other competitors had a conniption, so the FCC decided to "Let the market decide".

Motorola, which was a semiconductor manufacturer made their C-QUAM decoder IC readily available and cheap. (comparably)
Due to sheer volume of the ICs on the market, C-QUAM won.

Kahn's ISB system was the best as far as I'm concerned.

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Wed 04, 2017 11:14 pm 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
Actually stereo am is not expensive. Rca/Belar had a system that is very simple and cheap. The most expensive is kahn isb as it is the most complex to generate but it is cheap at the receive side as you could use 2 radios to listen to it in stereo. The biggest reason is the fcc wanted to help fm get started so they held am back untill it got late in the game. Now cquam and harris are more complex on the receive side but they both have chip sets so again cheap. The main thing was also the nafmb part of the nab also didnt really want it to take off because the investment in fm was already extensive. Fm is far more expensive to operate to cover a population center since you need both power and height and both are costly. A 100kw fm station at nearly 2000 feet up cant compete with am full power am or even less. The fm will need a transmitter in the neighborhood of 20kw or more . There are a few exceptions but the on i was involved with want but 500 feet up and ran 17.5 kw. Less line loss and 10 bays of antenna. Coverage wasnt very good for all that money and we owned the tower. The 5 kw am beat the pants off the fm. A 25 kw am on a poor frequency in the 1300-1400 part of the band covers parts of 4 states and in the daytime can be heard from milton florida its home all the way into new orleans loud and clear and all the way into texas inland listenable. An fm has no hope of that kind of coverage on a regular basis. Am stereo had its problems but the biggest one was the stations who had it didnt promote it well if at all. The receiver manufacturers should have been given minimum requirements to make the public get served a quality product. Do not tell me the fcc couldnt do this as they did for tv more than onece. The big broadcasters and the fcc did not want it to succeed this is clear.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Wed 04, 2017 11:34 pm 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
As far as the systems go they all have ups and downs. Kahn to properly encode and decode is the most expensive and it has a major problem with seperation consistency due to the fact that the audio filters needed to phase shift the audio to generate the independent sidebands are difficult to make without errors. Cquam and Harris are the closest to being 100% compatible with an envelope detector but harris was more involved as it used synchronous detection for all components wich is very good on specs but expensive and complex circuitry before chips. Cquam same thing as harris but uses envelope detection for l+r and has platform rotation issues. Magnavox a cousin to rca and belar are all simple. Rca/belar are the same system. It is simply narrow band fm of the am carrier with a high pre emphasis on the l-r channel. Magnavox was phase modulation of the l-r and fm and pm are kissing cousins in that the receiver in both cases uses the exact same demodulator methods. In fach a pll will decode all of them. Sony had several multi system radios that used this approach and detected the l+r with an envelope detector. They had a phase shift in the audio before matrixing it to decode kahn with propper soundstage results but they didnt have a true kahn decoder in those radios. All of the am stereo systems are phase/frequency modulation schemes with relatively small differences. The big problem for kahn technically and I talked with Leonard about it many times was related to the filters and the separation at different frequencies shifted in tests. It had the one advantage that am am station could modulate to almost 100% negative modulation peak where as the other systems required it to be limited to between 90 and 95 % for them to work properly. Radio stations always want to keep their mod up as high as possible for loudness reasons and competition reasons never mind quality. here is a link to a site that has a transmitter you can try.

http://electronbunker.ca/eb/AM_StereoXMTR.html

The fellow posts on this site as well.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 05, 2017 12:24 am 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 13827
Location: Dayton Ohio
True, back in the 60s, AM Stereo receivers would need special considerations.

Either sideband filters or I-Q phasing techniques, which is very easily done today.
With DSP and software defined receivers, its a snap.

That 3 tube AM Stereo transmitter is beautifully done! Its giving me inspiration!

Thanks for pointing it out!

Indiana Radios (Michael) has a solid state AM Stereo transmitter he's brought to shows before. Pretty cool!

-Steve

P.S. Do I really need another project in the queue? :-|

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 05, 2017 5:38 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
Here is the story and the diagram for the rca stereo system very simple and I have tried it and it works very well just can not modulate the l+r all the way to 100% negative or it punches holes in the l-r with todays processors it is easy to control that and go to 125% positive and 95% negative works great if you broadband the I.F. There were am radios with good bandwidth that adding this to is wonderful. Get a eico hft94 and mod it for stereo you will be amazed at it in wideband mode and it can be aligned to widen it further and it is a pleasure to listen to. The radio they moded was a basic design normal aa5 type.

http://www.fmamradios.com/RCA-AM-Stereo.html


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 05, 2017 10:09 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1936
Location: Saskatoon
I know at least a couple of AM music stations in my area that continue to broadcast in stereo. They would have converted to stereo back in the 1980's when stereo was introduced, and if they haven't seen any need to change their hardware since then, then they continue to broadcast in stereo. It doesn't cost them any extra, and from what I've seen, there are still lots of people driving around in their 1980's cars listening in stereo. So, why change?


Audioman wrote:
here is a link to a site that has a transmitter you can try.

http://electronbunker.ca/eb/AM_StereoXMTR.html

The fellow posts on this site as well.


That would be me. :P

I found your comments on AM stereo to be very interesting and very even handed. (It's surprising how biased the discussions can become when discussing AM stereo.)

The transmitter that I built depends on the fact that, other than the frequency of the pilot signal, there is almost no practical difference between the Magnavox system and the Motorola CQuam system (I have many vector diagrams to demonstrate this). If you're willing to accept a very small reduction in stereo separation, the circuit complexity drops drastically. Hence, just 3 tubes. And interestingly, if you use controlled carrier modulation as I did, you can, in fact, get net modulation greater than 100%


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 05, 2017 12:29 pm 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 13827
Location: Dayton Ohio
I apologize if my comments seemed biased.

I've not had much experience in listening to AM stereo short of C-Quam and hearing a Kahn system with two AM radios.
I remember when AM stereo was coming onto the scene as was quite excited about it, but then it seemed to stagnate. I was disappointed.
I used to travel quite a bit to Chicago with my 1987 Dodge Charger and listen to 670 WMAQ on the way in to catch traffic reports.

The "Platform motion" was incredible! The sound swished from side to side dramatically!
I was more amused about it rather than upset, but it certainly isn't a good thing. (BTW, I kept that radio. But it has faulty button switches now)

I wish I could have heard the other systems, but it seems broadcast engineers (from what I've heard) favored the Kahn ISB system.

Bob, may I congratulate you on such a beautifully designed and crafted chassis! I'm most impressed!
I've tried similar ideas on a couple audio amplifiers I built, but you have me beat! :D

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 05, 2017 7:49 pm 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
CQUAM had an advantage in that it was more compatible with an envelope detector in terms of lower distortion but if the station did not modulate quite as heavily then that was moot unless you are doing lab tests. The platform rotation is due to the need to use a pll to decode it and the pll may loose lock and round we go. The magnavox system and rca/belar do not need a pll to demodulate. Then can be decoded with the receiver I linked to with modification to the matrix. As far as the transmitter I linked to it can provide good separation and improved if the slight delay between l+r and l-r. These refinements can make things complex with little return. The magnavox system was originally picked by the fcc as the standard. Politics and egos got involved and so it went. If it were a world where very high precision parts were cheap kahn would then be able to compete but although it works better than the others this only holds for midrange audio frequencies due to the phase shift issues of the networks needed to obtain the +45 and -45 degree shift across the entire audio band. CQUAM and HARRIS have a group delay issue the the exciters have settings for. So make your trade off but at this time the chip sets are out there and reasonable on pre made boards so you cn add CQUAM to your radio and use the magnavox type encoder for true stereo. I have a real broadcast exciter for CQUAM so that is what I have in service here. You can make tube type decoders using what is in the rca radio I linked to or a modified version of it. You can also use a quaderature detector just like tv sets had and they work well too. Am stereo is an experimenters playground so get in here and have fun with it.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Fri 06, 2017 10:25 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1936
Location: Saskatoon
azenithnut wrote:
I apologize if my comments seemed biased.


Oops, sorry Steve, my comment about biased discussions of AM stereo wasn't directed at you. It was a general comment about what I've seen on various message boards.

By most accounts the Kahn system did give better sound quality. We had one local station that used the Kahn system briefly, but I never had a chance to give it a listening test, because by the time I'd acquired an AM stereo capable receiver, they had already switched over to C-Quam, as did everyone else.

Motorola was in an ideal position, since they had their own semiconductor division, and could supply the decoding chips as well as the transmitter hardware. They took great advantage of this.

National Semiconductor had developed the LM1981 decoding chip for the Magnavox system, since the FCC had initially only approved the Magnavox system. As far as I know, their decoder chip never went into production and there were only some samples made.

When I built my AM stereo transmitter, I did a lot of digging through the available tech literature, including Motorola's C-Quam patent. The one thing that I found very suspicious about the Motorola patent is that typically a patent will list prior art, and then list the current patent's improvements over the prior art. However, while the Motorola patent claimed to have several improvements over the existing Magnavox and Belar systems, they conveniently neglected to mention what these improvements are.

Okay, now I'm sounding biased. :)


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Sat 07, 2017 3:54 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 208
Location: pensacola fl
In simpler terms kahn had a soundstage / seperation thing going on at the extremes of the human hearing range. The position was different for the same sound source depending on the frequency content. Many times the bass end would become mono before 50 hz never mind all the way down to 20 hz. Same happened at the high trebble from about 8 khz up things started to shift and or blend back to mono. This was due to component precission and the fact that a filter doesnt have a constant phase shift across the entire audio range so the filters could not track precisely at the transmitter or receiver and so that is the way it was. Even digital filters are far from perfect. But as I said you can modify an older tube tuner/radio to try the stereo systems easily as compared to fm that was much harder unless the tuner was made to pass the mpx signal with its up to 53khz baseband and that had to be flat or stereo suffered.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Thu 12, 2017 4:27 am 
Member
User avatar

Joined: Apr Thu 19, 2012 6:50 am
Posts: 931
Location: Connecticut
We still have a station here in central Connecticut broadcasting AM stereo with a full service music format.1220 WQUN in Hamden sounds great on my homemade 1980's Delco car radio boombox.


Top
 Profile  
 
 Post subject: Re: AM Stereo Still Around?
PostPosted: Jan Sat 14, 2017 7:34 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1936
Location: Saskatoon
Audioman wrote:
In simpler terms kahn had a soundstage / seperation thing going on at the extremes of the human hearing range. The position was different for the same sound source depending on the frequency content. Many times the bass end would become mono before 50 hz never mind all the way down to 20 hz. Same happened at the high trebble from about 8 khz up things started to shift and or blend back to mono. This was due to component precission and the fact that a filter doesnt have a constant phase shift across the entire audio range so the filters could not track precisely at the transmitter or receiver and so that is the way it was. Even digital filters are far from perfect. But as I said you can modify an older tube tuner/radio to try the stereo systems easily as compared to fm that was much harder unless the tuner was made to pass the mpx signal with its up to 53khz baseband and that had to be flat or stereo suffered.


This is what I've heard as being the primary disadvantage of the Kahn system. If everything was perfectly calibrated, it gave the best performance, but if things went off slightly, then it fell apart badly. The other systems may not have been quite as high quality, but they were more tolerant when things went off spec.

Actually, I've learned more from bad signals than I've learned from good signals. We have no local AM-stereo stations, but there's one that's 130 miles away. Listening to that station during interesting atmospheric conditions gave me a good understanding of the platform rotation effect. If I hadn't been feeling my best, I might have been dashing to the bathroom to offload my supper.

(This also resolved a curious shifted center channel problem that I'd been trying to figure out on my own low power AM stereo transmitter project. Now I need to update my website about this.)


Top
 Profile  
 
Post New Topic Post Reply  [ 23 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests



Search for:
Jump to:  




















Privacy Policy :: Powered by phpBB